On This Day in Telephone History, February 29TH 1876, Alexander Graham Bell’s lawyer submitted a Patent Amendment, distinguishing Bell’s February 14TH patent from Gray’s caveat.
Bell’s lawyer telegraphed Bell, who was still in Boston, to come to Washington, DC. When Bell arrived on February 26, Bell visited his lawyers and then visited examiner Wilber who told Bell that Gray’s caveat showed a liquid transmitter and asked Bell for proof that the liquid transmitter idea (described in Bell’s patent application as using mercury as the liquid) was invented by Bell. Bell pointed to an application of Bell’s filed a year earlier where mercury was used in a circuit breaker. The examiner accepted this argument, although mercury would not have worked in a telephone transmitter. On March 3, Wilber approved Bell’s application and on March 7, 1876, U.S. Patent 174,465 was published by the U.S. Patent Office.